Dermatological picosecond laser treatment systems and methods using optical parametric oscillator

ABSTRACT

Dermatological systems and methods for providing a picosecond laser treatment a plurality of treatment wavelengths, at least one of which is provide by an optical parametric oscillator (OPO) capable of providing picosecond laser pulses at a wavelength in the red region of the visible electromagnetic spectrum for treating one or more target tissue types. In some embodiments, the OPO is capable of providing picosecond laser pulses at a wavelength in one of the near-infrared and the infrared region of the electromagnetic spectrum.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/820,421 filed on Nov. 21, 2017, entitled “Dermatological PicosecondLaser Treatment Systems and Methods Using Optical Parametric Oscillator”which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of electromagnetic-baseddermatological treatment systems, and more specifically to systems andmethods for treatment of dermatological conditions with lasers having atleast one wavelength determined by an optical parametric oscillator.

A variety of dermatological conditions are treatable usingelectromagnetic radiation (EMR). Sources of EMR for such treatmentsinclude lasers, flashlamps, and RF sources, each of which has distinctadvantage and disadvantage profiles. EMR devices have been used, forexample, treating abnormal pigmentation conditions, body sculpting(e.g., removal of subcutaneous adipose tissue), hair removal, treatmentof vascular skin conditions (e.g., spider veins), reduction of wrinklesand fine lines, and dyschromia, among other conditions. Abnormalpigmentation conditions may include tattoos and benign pigmented lesionsassociated with high local concentrations of melanin in the skin, suchas freckles, age spots, birthmarks, lentigines, and nevi, among otherpigmentation conditions. Both pulsed and continuous-wave (CW) lasersystems have been used to treat pigmentation conditions, although pulsedlasers are more frequently used.

Nanosecond lasers have been used for decades to treat pigmented lesionsand tattoo removal. Nanosecond lasers, as used herein, are pulsed lasershaving a pulse width (PW) or duration of greater than 1 nanosecond(nsec) up to 1 microsecond (μsec). By delivering the laser energy in apulse with a very short time duration, highly localized heating (anddestruction) of a tissue target structure (e.g., melanin, ink particles,collagen) can be achieved, thereby minimizing damage to non-targetstructures. Heating in tissues depends upon both the absorptioncoefficient of the irradiated tissue structures for the wavelength oflaser light used, as well as their thermal relaxation times (TRT), whichis a measure of how rapidly the affected structure returns to itsoriginal temperature. So long as the laser pulse duration is less thanthe thermal relaxation time of the target, no significant heat canescape into non-target structures, and damage to non-target structuresis limited.

The availability of picosecond laser pulses has ushered in a newparadigm in tattoo removal. As used herein, picosecond lasers are pulsedlasers having a pulse width or duration of 1 picosecond (psec) up to(and preferably below) 1 nsec. Studies have shown that the diameter oftattoo ink particles can range from 35 nm to 200 nm, with clusters aslarge as 10 μm. To clear the tattoo ink, the particles must be broken upinto smaller fragments that can be cleared by the body. To break theparticles up effectively, the laser energy must be delivered within theTRT of the particle, since the energy that escapes into the surroundingtissue not only damages non-target structures but also is unavailable tobreak down the target structure. A simple dimensional analysis showsthat the TRT of a spherical particle scales with the square of itsdiameter, and ink particles smaller than about 150 nm will haverelaxation times below 1 ns.

While the pulse duration for nanosecond lasers is generally less thanthe TRT for melanin in the skin, the small size of many ink particles intattoos can result in TRT times of less than 1 nanosecond for thoseparticles. Consequently, the use of conventional Q-switched nanosecondlasers, which produce pulses of 5-20 nsec in duration, may result inineffective ink removal as well as damage to tissue structures such asblood vessels, collagen, and melanin as the pulsed laser energy escapesinto adjacent non-target tissue structures after the lapse of the TRT.This is particularly true for lasers having wavelengths that are highlyabsorbed by the non-target structures. Studies have shown that the useof picosecond lasers instead of nanosecond lasers can reduce the numberof treatment sessions required to clear tattoos by a factor of 3.

Treatment of tattoos and pigmented lesions with picosecond laser pulsesis a new and rapidly developing field in dermatology. Althoughnanosecond lasers are in theory should be adequate for removal of benignpigmented lesions because the relaxation time of melanin is greater thanthe pulse width for many nanosecond lasers, physicians have reportedthat lower treatment fluences are required when using picosecond laserpulses, which reduces thermal loading to tissue and the risk of adverseevents. Thus, picosecond laser pulses may offer less tissue damage andhigher safety margins for pigmented lesions, in addition to theirsuperior performance for tattoo removal. The potential for improvedclinical outcomes using picosecond lasers has resulted in commerciallyavailable systems having pulse widths of 500-1000 psec with pulseenergies (i.e., energy per pulse) exceeding 100 mJ. On the other hand,high-energy picosecond lasers are much more complex and costly than anyother energy-based treatment systems in the dermatology market today,and there is a need for more flexible, less expensive picosecond lasersystems.

Tattoo removal presents a number of distinct challenges for laser-basedpigmentation treatment systems. Tattoos are created by depositingthousands of ink particles below the epidermis into the dermis of theskin. The depth of ink particles may range from 250-750 μm, or morecommonly 300-500 μm. In some instances, however, ink depths up to 1800μm may occur. The wide particle size distribution, as already noted,also presents a challenge for effective tattoo removal while minimizingdamage to surrounding structures.

Lasers remove tattoos by breaking down the ink particles that form thetattoo design with laser light at a wavelength that is highly absorbedby the ink used in the tattoo, and at a fluence (energy per area,typically expressed as J/cm³) sufficient to rupture the ink particlesinto smaller particles that can be removed by the body's natural repairsystems.

Ink colors are determined based on their light absorption profile. Agiven color results from the ink absorbing complementary colors oflight, i.e., colors opposite to the ink color on a color wheel. Forexample, because red and green are complementary colors, green inksappear green to the eye because they absorb colors in the red area ofthe visible light spectrum, while red inks appear red because theyabsorb colors in the green area of the visible light spectrum. Thus,green inks are more efficiently removed by red light, since green inkhas a relatively high absorption of its complementary color. Conversely,red inks are best removed by green light because they highly absorblight in the green wavelengths.

Tattoos incorporating multiple ink colors present special challenges inlaser-based removal systems, because multiple laser wavelengths may benecessary to remove all of the different ink colors. Thus, multiplelaser sources may be used in some systems, resulting in systems that aremuch more expensive, complex, and bulky. To avoid damage to the skinbecause of the high energy fluences involved, many systems allow a userto vary the width of the laser beam applied to the tattoo.

Shading in tattoos presents another challenge to safe and efficienttattoo removal. Shading results in significant variations in the inkparticle density (i.e., color intensity variation) across the tattooarea. Because of this, some systems allow a user to vary the pulse width(PW) of pulsed laser systems, also adding to the complexity of thesystem. In addition, because the ink particles may be located atdifferent depths within the dermis, it is preferable for the laser lightto have a high fluence even at relatively large beam diameters.

The first commercial dermatological picosecond laser systems used eithera single 755 nm lasing wavelength, with alexandrite as the lasingmedium, or dual 1064 nm and 532 nm laser wavelengths using Nd:YAGlasers. The 755 nm and 1064 nm wavelengths are part of the near-infraredportion of the electromagnetic spectrum, and are well-suited to removalof black tattoo inks due to their broad absorption spectra. The 532 nmwavelength is in the green portion of the visible spectrum, and iswell-suited to removal of red inks which strongly absorb green light(the complementary color of red).

Because black and red are the most common tattoo colors, dual wavelength(532 nm and either 755 or 1064 nm) picosecond systems are the mostcommon systems available. However, green and blue inks occur in aboutone-third of tattoos, and the absorption strength for these inks isgreatest in the red portion of the visible spectrum. Accordingly, thereis a need for a red wavelength in addition to the dual wavelength1064/755, 532 nm (near infrared and green) picosecond laser systems tofacilitate removal of green and blue inks. In view of the already-highcost of picosecond laser systems, the addition of a red wavelength mustbe done at a low cost, and in a flexible system that allows differentwavelengths of light to be selected quickly and easily.

Because of their versatility, dual wavelength (1064/755, 532) picosecondsystems are widely used to treat benign pigmented lesions, which involvethe removal of melanin particles from the skin. Pulsed light at 532 nmis highly absorbed by melanin, while 1064 nm light absorbed less than10% as well (absorption coefficients of 55.5 mm⁻¹ and 4.9 mm⁻¹) poorlyabsorbed. In addition, penetration depth of laser light falls rapidlywith wavelength. Therefore, 532 nm laser light is effective ataggressive treatment of shallow pigment and 1064 nm light is morecommonly used for milder but deeper treatment. It would be useful tohave a third wavelength with an intermediate absorption in melanin.

Treatment of pigmented lesions can sometimes result in post-inflammatoryhyperpigmentation or hypopigmentation. While the reason for such adverseevents is uncertain, it is believed that this may result from injury ofthe laser light to blood vessels. Accordingly, effective wavelengths fortreatment of pigments are those that minimize potential damage to bloodvessels in the superficial dermis, and maximize the absorption ofmelanin relative to hemoglobin.

Pulsed red light has been provided in prior art laser systems, bylaser-induced florescence of organic dyes. Typically, excitation isprovided by a 532 nm (green light) Nd:YAG pulsed laser, with the redemission wavelength determined by the specific dye being used.Wavelengths of 585, 595, and 650 nm have been provided. Dyes aresometimes provided embedded in a sold substrate. In systems of thistype, the minimum pulse duration is defined by the fluorescence lifetimeof the dye, which is typically between 1-5 ns, precluding their use inpicosecond laser systems. Incoherent (non-laser) light may be capturedoptically and focused onto a treatment plane.

In other systems, the dye cells may be used as the gain medium in alaser cavity to produce laser emission, in which case picosecond pulsesare possible because the pulse duration is approximately equal to thatof the excitation laser. However, the cost of assembling such systems issignificantly increased relative to systems that do not require dyes,and becomes prohibitive if the dye cells must be replaced frequently.

A more fundamental limitation of dye systems is their susceptibility tooptical degradation. Both output energy and beam profile uniformity fallrapidly with operation, typically within 10,000 laser shots or pulses.Fluence of the beam at the treatment plane therefore becomes irregularand continues to change over time, leading to poor clinical outcomes.Emission also tends to have low spatial coherence, making it difficultto deliver the beam through a fiber or articulated are to an applicator,such as a handpiece, for application to the patient.

Because of optical degradation issues, dye cells are typically designedas a consumable item that attaches to the end of the applicator (e.g., ahandpiece). While this allows the user to change the dye cell whenperformance drops, restoring beam uniformity and fluence, it introducesseveral limitations. First, in multi-wavelength systems the dye cellmust be removed to change wavelengths, which is inconvenient to the userand patient during removal of multi-colored tattoos requiring multiplewavelengths in a single treatment session. Second, because the dye cellis near the point of application, integration of photometry to detectthe optical degradation is difficult because of space limitations. Inspite of these limitations, dye cells have seen limited but consistentuse in the field for decades because of their ability to providemultiple laser wavelengths.

Another known method for generating red-wavelength picosecond laserpulses is through second harmonic generation, in which the frequency ofthe pumping laser is doubled, resulting in an output having wavelengthsthat are half that of the pumping laser. For example, Nd:YAG lasingwavelengths such as 1319 or 1338 nm may be frequency doubled withnonlinear crystals to produce red picosecond pulses at 659 and 669 nm.However, pumping wavelengths capable of frequency doubling to providered laser light have relatively low optical gain, making the cost andcomplexity at these wavelengths significantly greater than existing 1064and 532 nm dual wavelength systems. In addition, wavelengths in the 1300nm range have limited use for dermatology, and such systems would haveonly one wavelength of significant value unless more than one laserengine is provided in the system, which would significantly increasesystem complexity, cost and bulk. Such systems are not economical andhave not been commercialized.

Finally, laser architectures outside of the red spectral region havebeen developed, but these systems sacrifice clinical efficacy because ofthe non-optimal wavelengths. For example, picosecond laser systems areavailable that produce 755 nm, near-infrared pulses using alexandrite asthe lasing medium, as well as systems that using 532 nm picosecondpulses to pump a titanium sapphire oscillator,

There is a need for dermatological picosecond laser systems that areable to efficiently remove tattoos that incorporate a variety of inkcolors, particle sizes and ink depths, and which are relatively compact,non-bulky and easy to use. There is also a need for dermatologicalpicosecond laser systems having a simplified construction with fewercomponents, which are capable of providing a variety of laserwavelengths for treatment of a wide variety of pigmentation conditionsand skin conditions, and allow a user to switch from a first to a secondtreatment wavelength quickly and easily.

SUMMARY

In one embodiment, the present invention comprises a dermatologicaltreatment system for removal of one or more of tattoos and pigmentedlesions using pulsed laser light, comprising: a laser engine constructedand arranged to output first laser pulses having a first wavelength offrom 1000 nm to 1200 nm, a first pulse width of 200 psec to 10 nsec, anda first pulse energy of from 100 mJ/pulse to 5 J/pulse; a secondharmonic generator (SHG) constructed and arranged to receive the firstlaser pulses from the laser engine and generate second harmonic laserpulses having a second wavelength that is half the wavelength of theamplified laser pulses; an optical parametric oscillator (OPO)constructed and arranged to receive the second harmonic laser pulses andgenerate OPO signal pulses having a third wavelength of from 630 nm to755 nm and OPO idler pulses having a fourth wavelength longer than thethird wavelength; and an applicator constructed and arranged to receiveand apply a selected one of the first laser pulses, the second harmoniclaser pulses, and the OPO signal pulses to the skin of a patient.

In one embodiment, the present invention comprises a dermatologicaltreatment system for treatment of at least one of a tattoo and apigmented lesion using pulsed laser light at one of at least threeselectable wavelengths, the system comprising: a laser engineconstructed and arranged to output first laser pulses having a firstwavelength of from 1050 nm to 1075 nm, a first pulse width of 200 psecto 1 nsec, and a first pulse energy of from 100 mJ/pulse to 5 J/pulse; asecond harmonic generator (SHG) constructed and arranged to receive thepulsed laser light from the laser engine and generate second harmoniclaser pulses having a second wavelength that is half the wavelength ofthe first laser pulses; an optical parametric oscillator (OPO)constructed and arranged to receive the second harmonic laser pulses asthe pump input to the OPO and generate OPO signal pulses having a thirdwavelength of from about 630 nm to about 720 nm and OPO idler pulseshaving a fourth wavelength longer than the third wavelength; and anapplicator constructed and arranged to apply one of the first laserpulses, the second harmonic laser pulses, and the OPO signal pulses tothe skin of a patient, the applicator comprising a selector to selectsaid one of the first laser pulses, the second harmonic laser pulses,and the OPO signal pulses.

In one embodiment, the present invention comprises an optical parametricoscillator (OPO) for use in a dermatological treatment system, whereinthe OPO produces OPO signal pulses having a pulse width of from 200 psecto 1 nsec and a wavelength of from 630 nm to 720 nm, and OPO idlerpulses having a fourth wavelength longer than the wavelength of the OPOsignal pulses, the OPO comprising: an input coupler comprising a mirrorhaving a high transmission (HT) at a pumping wavelength and a highreflectance (HR) at the OPO signal wavelength; a nonlinear crystalhaving a crystal length between 5 and 25 mm; and an output couplercomprising a mirror having a high reflectance (HR) at the pumpingwavelength that transmits a selected portion of the OPO signalwavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional illustration of skin tissue.

FIG. 2 is a graph illustrating the frequency of use of inks of variouscolors in tattoo designs.

FIG. 3 is a color wheel illustrating various colors and theircomplementary colors.

FIG. 4 is a graph illustrating the absorption spectra of red, green,blue, and black ink for various wavelengths of light.

FIG. 5A is a graph illustrating the absorption coefficients of melanin,venous blood, and arterial blood for various wavelengths of light.

FIG. 5B is a graph illustrating the melanin to blood absorption ratiofor venous and arterial blood for various wavelengths of light.

FIG. 6 is a block diagram of a system for treatment of dermatologicaltissue using pulsed laser light according to one embodiment of thepresent disclosure.

FIG. 7 is a block diagram of a prior art optical parametric oscillatorsuitable for use in dermatological treatment systems with nanosecondlasers.

FIG. 8 is a diagram of one embodiment of the optical parametricoscillator of FIG. 6.

DESCRIPTION

Exemplary embodiments of the present disclosure are illustrated in thedrawings, which are illustrative rather than restrictive. No limitationon the scope of the technology, or on the claims that follow, is to beimplied or inferred from the examples shown in the drawings anddiscussed here.

The present application discloses systems and methods for treatment of avariety of dermatological conditions using lasers, including systemsproviding a plurality of different wavelengths of laser light to provideimproved therapies for certain skin pigmentation conditions, with atleast one of the wavelengths being determined by an optical parametricoscillator. In some embodiments, systems of the present disclosurepermit rapid adjustment from a first treatment wavelength to a secondtreatment wavelength.

Embodiments of the invention involve systems and methods for one or moreof treating a pigmentation condition in human skin (including withoutlimitation removal of tattoos and benign pigmented lesions) and skinresurfacing (including without limitation treatment of acne and otherscar tissue) using pulsed laser light having a high peak power (i.e.,power per pulse). Multiple wavelengths of laser light suitable for usein such systems and methods may be provided using an optical parametricoscillator (OPO).

In one aspect, a system capable of providing picosecond laser pulses atthree or more different wavelengths suitable for treating pigmentationconditions and/or skin resurfacing is provided. In one aspect, a systemcapable of providing picosecond laser pulses at a plurality ofwavelengths for treating pigmentation conditions and/or skin resurfacingusing an OPO is provided. In one aspect, a system capable of providinghigh-energy, picosecond laser pulses at a plurality of wavelengths,including a red wavelength, is provided in a manner that allows a userto select one of the plurality of wavelengths quickly and easily.

In one aspect, a system capable of providing high-energy picosecondlaser pulses at a red wavelength is provided in a manner that may beadded to an existing picosecond laser system. In one aspect, a systemfor providing picosecond laser pulses at a red wavelength, capable oflong-term operation without loss of output energy or beam uniformity isprovided. In one embodiment, the system is capable of provided more than1 million laser pulses without significant loss of output energy or beamuniformity. In one aspect, a tunable OPO capable of use in adermatological picosecond laser system is provided that allows a user toselect any desired wavelength within a range of 630-755 nm, preferably630-720 nm, more preferably 660-680 nm, more preferably 665-675 nm, andmore preferably about 670 nm.

In one aspect, methods for providing a dermatological treatmentaccording to one of the foregoing systems is provided.

FIG. 1 is a side view illustrating a cross-sectional view of a portion100 of the skin of a patient, including the outermost epidermis 110, themiddle layer or dermis 120, and the bottom layer or hypodermis 130. Theepidermis 110 has a thickness of about 80-100 μm, which may vary frompatient to patient and depending on the area of the body. It includes upto five sub-layers and acts as an outer barrier. The outermost layer(the stratum corneum) consists of dead skin cells, which are constantlybeing replaced by new cells being made in the bottom layer (the stratumbasale).

The dermal layer has thickness of about 1-5 mm (1000-1500 μm). The inksin a tattoo design and the melanin in a pigmented lesion are bothlocated in the dermis. Consequently, laser light for removing tattoosand pigmented lesions must penetrate into the dermis. The dermiscontains the blood vessels, nerves, hair follicles, collagen and sweatglands within the skin. Careful selection of a number of parameters mustbe made avoid damaging many of these structures in the design andconstruction of laser systems for removal of tattoos and pigmentedlesions. For example, incorrect selection of the laser wavelength, pulsewidth, energy per pulse, the use (or nonuse) of a seed laser, or thepump energy of the laser source or amplifier may result in damage to oneor more of the foregoing structures in the dermis, as well as poorperformance in removal of the tattoo or pigmented lesion. Numerous othersystem choices, such as the use or non-use of an articulating arm fordelivery of the laser light to a handpiece for application to thepatient's skin, may also result in tissue damage and/or poor systemperformance if careful selection is not made.

The lowest layer of the skin is the hypodermis, which includes adiposetissue and collagen. The hypodermis helps control body temperature byinsulating the structures of the body below the skin. In addition, thehypodermis protects the inner body tissues from damage by absorbingshock and impacts from outside the body. Because the hypodermis containsfat, its thickness varies widely from person to person based on diet,genetic makeup, and other factors.

FIG. 2 is a graph illustrating the frequency of ink use of certaincolors in tattoo designs. Although black ink is the most frequently usedcolor in tattoo designs (79% of tattoos), red ink is the next mostfrequently used color, appearing in about 45% of tattoo designs. Darkblue ink is used in about one third (34%) of tattoos, followed closelyby yellow (32%) and green (30%) inks, respectively. Light blue ink isused in about one-fourth (25%) of tattoo designs.

FIG. 3 is a color wheel demonstrating the concept of complementarycolors, which are the colors opposite to a given color on the colorwheel. Thus, as previously noted, inks are more efficiently removed bylaser light of a complementary color. Because of the prevalence of greenand blue inks, it is desirable to have a system capable of reliablyproducing a red light wavelength in addition to the more widelyavailable 1064 nm and 532 nm wavelengths.

The light absorbance profile of a substance is determined by thechromophores (i.e., the light-absorbing portions of molecules) within itthat absorb light at particular wavelengths within the EMR spectrum. Thecolor of a substance (e.g., skin) is determined by the absorbanceprofiles of the chromophores within the visible light portion of the EMRspectrum. Sunlight, although seen as a homogenous white color, is acomposite of a range of different wavelengths of light in theultraviolet (UV), visible, and infrared (IR) portions of the EMRspectrum. A substance appears to the eye as the complementary color ofthe light wavelengths that are absorbed.

Laser-based removal of pigmentation occurs by applying light at highfluences (i.e., energy per unit area) such that thechromophore-containing compounds within the pigmented area (e.g., inkparticles in a tattoo or melanin in freckles or age spots) absorb somuch energy that the ink or melanin particles in the pigmented area areruptured or broken into small particles that may be removed by the body.

The more highly absorbed the wavelength of laser light by melanin (inthe case of pigmented lesions) and/or inks (in the case of tattoos), themore efficient the removal. Stated differently, less energy must bedelivered to rupture an ink or melanin particle if the wavelength of thelaser light being used is highly absorbed by the ink in the tattoo orthe melanin in the pigmented lesion. The absorption profile is only oneaspect of laser wavelength selection, however, and a wide range of laserwavelengths are used to remove tattoos and pigmented lesions, includingwavelengths in the visible and near-IR spectrum. Commercially availablesystems for removal of tattoos and pigmented lesions have used laserlight at 532 nm, 597 nm, 650 nm, 755 nm, 785 nm, and 1064 nm, amongothers.

FIG. 4 is a graph illustrating the absorption curves for various tattooink colors at a range of wavelengths. As previously noted, black ink(“ebony black”) has a high absorbance across a wide range of laserwavelengths. Accordingly, black ink in tattoos may be efficientlyremoved using a variety of different laser systems and wavelengths.

FIG. 4 also shows that red ink (“ruby red”) has a high absorbance at 532nm and nearby wavelengths, but its absorbance falls rapidly at higherwavelengths. Consistent with the concept of complementary colorsdiscussed earlier, the 532 nm wavelength corresponds with green light inthe visible spectrum, which is the complementary color of red.Accordingly, red light may be removed efficiently by 532 nm green laserlight but is poorly removed by, for example, 670 nm light in the redlight portion of the visible spectrum.

Conversely, FIG. 4 shows that green ink (“forest green”) has a highabsorbance of 660-670 nm red light. Thus, tattoos with green ink aremuch more effectively removed by 660-670 nm laser light that, forexample 532 nm green light, which is very poorly absorbed by green ink.Although green ink has a reasonable absorbance of near-infrared light at755 and 785 nm (absorbance of about 0.6 and 0.5, respectively), it hasmore than 50% greater absorbance at 660-670 nm wavelengths(absorbance >0.9) in the visible red portion of the spectrum.Accordingly, 660-670 nm red laser light may provide for removal of greeninks in tattoos with reduced laser intensity or fluence, fewertreatments sessions, or both, than green or near-infrared wavelengths.

FIG. 4 also illustrates that 660-670 nm red light will more efficientlyremove blue inks (“royal blue”) than near-infrared wavelengths such as755 and 785 nm. Although not as strongly absorbing of red light as greeninks, blue inks similarly show a much stronger absorption at a 670 nmwavelength than at 755 and 785 nm near-infrared (˜40% greater absorbancethan 755 nm wavelength and ˜50% greater absorbance than 785 nmwavelength). Accordingly, 660-670 nm red light offers improved removalof blue inks than current widely used wavelengths.

FIG. 5A is a graph illustrating the absorption curves for venal andarterial blood and melanin at various wavelengths of light. For removalof pigmented lesions, it is desirable to target melanin in the skin tothe exclusion of other structures, notably blood and blood vessels.Greater safety may be provided by wavelengths that are poorly absorbedby non-target structures. FIG. 5A illustrates that melanin is stronglyabsorbent at lower wavelengths of light in the red visible wavelengthsaround 650, but its absorbance decreases steadily to a very lowabsorption in the near-infrared region. The absorbance of venous andarterial blood, on the other hand, decrease rapidly from 600 nm throughabout 650 nm. Arterial blood (lower curve) decreases rapidly until arelatively flat absorbance profile in the range of 630-700 nm, with aminimum value around 680 nm. Venous blood decreases rapidly to about630-640 nm, then decreases more slowly to a minimum value at around 730nm.

Maximum safety margin is provided at wavelengths having the maximumdistance between the absorption curves of melanin on the one hand andvenous/arterial blood on the other. This occurs between about 670 nm andabout 700 nm, indicating that red laser light in this range willminimize damage to blood and blood vessels in the treatment of pigmentedlesions. Thus, it would be desirable to add a red laser light capabilityto existing 1064/532 nm dermatological systems.

FIG. 5B illustrates this in another way by graphically indicating theratio of the absorption ratios of venous and arterial blood to melanin.As the arterial blood curve demonstrates, melanin has its maximumabsorption relative to arterial blood at a wavelength slightly above 670nm. For venous blood, melanin reaches its relative peak at about 700 nm.Accordingly, red light in the 670-700 nm range, in addition to providingimproved removal of green and blue tattoo inks, also offers potentiallygreater safety in removal of pigmented lesions.

In one embodiment, systems of the present invention may provide pulsedlaser light at one or more wavelengths selected for efficient removal oftattoos having a wide range of ink densities. In one embodiment, a usermay select a wavelength within a desired range for at least a portion ofthe wavelength output range that the system is capable of producing. Inone embodiment, the laser pulses of the system have a pulse energyranging from 100-1500 mJ/pulse. In one embodiment, the laser pulses ofthe system have a peak power of 250 megawatt (MW) or higher, preferably500 MW or higher, more preferably 1 GW or higher. In one embodiment, adermatological treatment system provides laser light at a fluence of upto 5.0 J/cm². In one embodiment, a user may select a spot size (e.g., byadjusting the diameter of a laser beam) for treating a pigmentationcondition.

Some embodiments of the present invention involve high-energy pulsedlasers and an optical parameter oscillator (OPO) to provide a variety ofselectable wavelengths for one or more of treatment of pigmentationconditions and skin resurfacing. Applicants have discovered that OPOsmay be used to generate a range of pulsed laser wavelengths useful inremoval of tattoos and benign pigmented lesions. Producing of suchwavelengths using an OPO, however, requires a laser capable of producingrelatively high-energy pulses. As used herein, the term “laser engine”refers to a pulsed laser system capable of producing pulses having apeak power of 250 megawatt (MW) or higher, preferably 500 MW or higher,more preferably 1 GW or higher.

FIG. 6 is a schematic illustration, in block diagram form, of adermatological laser treatment system 600 using high-energy pulsed laserlight according to the present disclosure. A laser engine 620 isprovided to produce high-energy pulsed laser light at a desiredwavelength. Although a number of different laser engines are describedin the present disclosure, the description herein of certain laserengines should not be construed as excluding others not specificallydescribed. It will be appreciated by persons of skill in the art in viewof the present disclosure that a variety of different materials, designsand techniques may be employed to generate high-energy pulsed laserlight in systems of the present invention. Unless specifically excludedby the scope of the claims, all are considered to be within the scope ofthe present disclosure.

Laser engine 620 outputs laser pulses having a wavelength of from 1000nm to 1200 nm, a pulse width (PW) of 200 psec to 10 nsec, and a pulseenergy (PE) of 100 mJ/pulse to 5 J/pulse. In view of the fact that thepeak power is given by the pulse energy divided by the pulse power orPE/PW, it will be appreciated that a variety of pulse widths and pulseenergies may be used to produced high-energy laser pulses at a desiredwavelength and having a peak power of 250 megawatt (MW) or higher. Inone embodiment, laser engine 620 is a Q-switched laser.

A second harmonic generator (SHG) 630 receives the laser pulses from thelaser engine 620 and generates second harmonic laser pulses with awavelength that is half that of the pulses received from the laserengine 620. Many different crystals may be used for SHG, which resultsin an output signal having double the frequency and half the wavelengthof the pumping signal. In the case of 1064 nm (fundamental) and 532 nm(second harmonic) wavelengths, potassium titanyl phosphate (KTP) andlithium tetraborate (LBO) are common choices, although other crystalssuch as potassium dihydrogen phosphate (KDP) may also be used. Thecrystals typically have a length between 2 and 15 mm. Depending on whichmaterial is chosen, the laser engine pulses received by the SHG may notrequire focusing to achieve efficient conversion to the second harmonic.

An optical parametric oscillator (OPO) 640 receives the pulses from theSHG and provides two pulsed laser outputs, known as the “signal” and“idler” respectively. Both OPO outputs (i.e., the OPO signal pulses andthe OPO idler pulses) comprise laser light having a wavelength longerthan the light received from the SHG 630. Optical parameter oscillatorsoperate by receiving a pump laser signal (e.g., pulses as a firstwavelength), which is used to induce parametric amplification within anonlinear crystal in the OPO to produce the two output electromagneticfields (i.e., the OPO signal pulses and the OPO idler pulses). OPOs aretunable over a wide range of wavelengths and potentially offer theability to produce any desired wavelength within a range of desiredwavelengths.

An applicator 650 is provided to receive pulsed laser light 655 from oneor more of the laser engine 620, the SHG 630, and the OPO 640, and applythe received laser pulses to the skin of a patient for treating apigmentation condition or skin resurfacing. The applicator may comprisea handpiece adapted to be held in the hand of a user, such as aphysician or other healthcare provider, for treating the patient withpulsed laser light 655.

In some embodiments, the applicator may also comprise a selector (e.g.,a touchscreen on the applicator) allowing a user to select the pulsesfrom one or more of the laser engine 620, the SHG 630, the OPO (640)signal, and the OPO (640) idler for application to the skin of thepatient. A first output path 660 is provided to direct the output oflaser engine 620 to the applicator 650. In the embodiment of FIG. 6,first output path 660 comprises an optical multiplexer 665 between thelaser engine 620 and the SHG 630 to direct the laser pulses from laserengine 620 to the applicator 650. A second output path 670 is providedto direct the output of the SHG 630 to applicator 650. In the embodimentof FIG. 6, an optical multiplexer 675 located between the SHG 630 andthe OPO 640 directs the pulsed SHG output to the applicator 650. A thirdoutput path 680 is provided to direct the OPO signal output to theapplicator 650. In the embodiment of FIG. 6, an optical multiplexer 685located at the OPO signal output directs the OPO signal pulses to theapplicator 650. In some embodiments, as shown in FIG. 6, a fourth outputpath 690 is provided to direct the OPO idler output pulses to theapplicator 650. In the embodiment of FIG. 6, an optical multiplexer 695located at the OPO idler output directs the idler output pulses to theapplicator 650. In some embodiments, optical multiplexer 695 is omitted.In some embodiments (not shown) a single optical multiplexer and outputpath may be provided for both the OPO signal pulses and the OPO idlerpulses.

In some embodiments, one or more of optical multiplexers 665, 675, 685,and 695 may be selectable by a user, e.g., by a rotatable mirror (notshown) from an interface located on the applicator 650, to allow theuser to choose one among a plurality of available wavelengths of lightto be routed to the applicator 650 to treat a patient. In addition,although the embodiment of FIG. 6 illustrates each of the first, second,third and fourth output paths, in alternative embodiments (not shown),one, two, or three of the four output paths shown may be omitted, suchthat pulses for one or more of the laser engine 620, the SHG 639, andthe OPO 649 may not be available to treat a user. Although not shown inFIG. 6, one or more beam dumps may also be selectable by a user to shuntthe laser pulses from one or more of the laser engine 620, the SHG 630,the OPO 640 signal output pulses, or the OPO 640 idler output pulses.

Although laser systems according to FIG. 6 may be constructed in anumber of different physical layouts, a housing or chassis (not shown)may be used to provide store and protect some or all of the foregoingoptical components. In one embodiment (not shown) a movable console(e.g., a wheeled cart) may function as a housing to house the laserengine 620, the SHG 630, the OPO 640, and the optical multiplexers 665,675, 685, and 695. In one embodiment, an articulated arm having anoptical medium (e.g., one or more waveguides) therein may be used toprovide an optical path for the optical multiplexers 665, 675, 685, and695 to direct pulses for a selected one of the laser engine 620, the SHG630, the OPO 640 signal output, and the OPO 640 idler output pulses tothe applicator (e.g., to a handpiece constructed and arranged to be heldin the hand of a user). In one embodiment, a movable console may beprovided as a housing to house the laser engine 620, SHG, and opticalmultiplexers 665 and 675, with the OPO 640 and optical multiplexers 685and/or 695 located in an applicator such as a handpiece.

Finally, a controller 605 is provided, together with appropriateelectrical circuitry, to control the operation of the dermatologicallaser treatment system of FIG. 6. In one embodiment, the controller 605controls the operations, including the electrical operations, of one ormore (and preferably all or most) of the laser engine 620, the SHG 630,the OPO 64, and applicator 650. In one embodiment, the controller 605controls the operations of one or more of the laser engine 620, the SHG630, the OPO 640, and multiplexers 665, 675, 685 and 695.

Laser engine 620 may comprise any of a number of designs to achievestable, high-energy pulses, and all such designs are intended to bewithin the scope of the invention. In one embodiment (not shown), laserengine 620 comprises a seed laser providing a pulsed initial lasersignal for further amplification by an amplifier. Seed lasers arefrequently used to produce a low power initial signal that may beamplified to obtain a final laser signal having desired characteristic.Many characteristics that may be desired in the final signal (e.g.,short pulse widths, a wavelength having a narrow spectral line width)are easier to produce in a seed laser than in a single, high-powerlaser. The seed laser signal may then be easily amplified to obtain alaser signal having desired characteristics.

Although many seed lasers produce pulses having a pulse energy of 1 μJor less, in one embodiment, a high-power seed laser is provided. Thehigh-power seed laser is capable of producing pulses of at least 100 μJper pulse, more preferably 100 μJ to 10 mJ, with a narrow linewidth anda wavelength of from 900-1200 nm, as well as a pulse width of 1 psec to100 nsec. In one embodiment, the seed laser produces pulses having astable polarity, and may be constructed and arranged to produce otherdesirable characteristics to enable the amplifier to output high-energyoutput pulses having a pulse energy of 100 mJ to 5 J, more preferably500 mJ to 5 J, a wavelength of 1000-1200 nm, and a pulse width of 200psec to 10 nsec. The pulses in seed laser have a relatively high peakpower that may be amplified to obtain high-energy pulses as required bylaser engine 620. In various embodiments, the seed laser may take theform of many oscillators known in the art to produce picosecond pulsesincluding fiber lasers, microlasers, or diode lasers.

The pulsed output of the seed laser is received by an amplifier (notshown), which amplifies the output of the seed laser to produceamplified laser light having the same pulse width and wavelength as theseed laser, but with a greater pulse energy. In one embodiment, theamplifier amplifies the seed laser pulses by a factor of 1000 or more.The amplified laser pulses output from the amplifier may, in someembodiments, be output (e.g., to an applicator such as applicator 650)and used to treat a dermatological condition of a patient. Multipleapproaches in the art are known for amplifiers that will amplify lasersignals to a pulse energy of >100 mJ, including >500 MJ.

In one embodiment (not shown), laser engine 620 may comprise a highpower oscillator. In one embodiment (not shown), laser engine 620 maycomprise a hybrid modelocked laser combining the functions of a laseroscillator and amplifier into a single cavity. Other approaches may alsobe used to produce appropriate laser engines 620.

There are a number of challenges to producing an OPO capable of pulseenergies of 50 mJ/pulse or greater for picosecond lasers. For optimizeddesigns, the conversion efficiency of pump light to output (signal andidler) is about 30-50%. Because of the high energies involved,relatively large beam diameters must be used to avoid exceeding thethreshold intensity to damage to optical structures within the OPO. Inaddition, the cavity length must be limited to enable the light to makeat least 10-30 round trips across the cavity during the pulse duration(or width) to enable the signal and idler fields to build up to maximumenergy. This results in a scaling law of about 1 cm/ns for the maximumcavity length vs. pump pulse duration. Thus, for a nanosecond laserhaving a pulse duration of 5 ns, the cavity length should be limited to5 cm or less. For a picosecond pulse, the cavity length should thus belimited to less than 1 cm. However, it is not possible to simply makethe cavity very small because cavity length is inversely related to beamquality, as explained below.

The combined constraints of large beam diameter and short cavity lengthimposed for achieving high pulse energies (50 mJ/pulse or greater) forpicosecond pulses creates a fundamental challenge for OPO performance,because they result in the cavity having a high Fresnel number,expressed as N=d²/(4Lλ), where N, d, L, and λ are Fresnel number, beamdiameter, cavity length and wavelength, respectively. Thus, because theFresnel number varies inversely with the cavity length L, the smallerthe cavity length, the larger the Fresnel number. It is well-known thatoptical cavities with N>>1 are prone to lasing many transverse opticalmodes, and therefore have low beam quality.

Beam quality in laser systems is typically expressed as M², whichprovides a measure of the spatial coherence of the beam and thereforehow well it can maintain collimation over a given distance. The largerthe value of M², the higher the divergence angle of the beam (i.e.,lower values indicate higher beam quality). The M² parameter is acritical measure for laser emission because it impacts the complexity ofthe optical delivery system design. For high energy picosecond medicallaser systems requiring an articulated arm to deliver the beam to theapplicator (e.g. a handpiece), the larger the value of M², the largerthe diameter of the arm required to accommodate the divergenceassociated with the deterioration of the beam quality.

An example of a proposed OPO design illustrates the problem. In an OPOdesign proposed by Rustad et al. (FIG. 7) loss of beam quality wasaddressed by using two nonlinear crystals C1 (730) and C2 (740) withorthogonally oriented beam walk-off axes and tuning of the signalwavelength to 670 nm to induce absorption of the idler pulses 770 in oneof the crystals. The Rustad design proposes a 5 nsec pulse 710 having aninput pulse energy of 120 mJ, a beam diameter of 6 mm, and a pulsewavelength of 532 nm. An input coupler mirror 720 is highly reflective(HR) at the 670 nm OPO signal wavelength and highly transmissive (HT) atthe 532 nm pump or input wavelength. An output coupler 750 has highreflectance (HR) at the 532 nm pump wavelength and 35% reflectance atthe 670 nm OPO signal wavelength, outputting OPO signal pulses 760having a pulse energy of approximately 50 mJ. OPO 700 also producesidler pulses 770, shown in FIG. 7 for illustration as being output fromoutput coupler 750 but which were, according to Rustad et al., absorbedwithin nonlinear crystals 730 and/or 740.

In simulations, Rustad et al. demonstrated that walk-off in orthogonalaxes and absorption of the idler signal within the crystals 730, 740 maybe combined to achieve a beam quality parameter M²≈2. Without idlerabsorption, the beam quality decreased to M²≈8. They also determinedthat the maximum efficiency is achieved when both crystals were 20 mmlong. The cavity had a Fresnel number of N=335, indicating that theRustad design significantly improved expected beam quality.

However, the Rustad et al. design is not well suited to use inpicosecond laser systems. Applying the foregoing scaling law for a 750psec pulse, the cavity is limited to less than 1 cm (about 0.75 cm inlength), which is insufficient length to provide two nonlinear crystalsof adequate length. More significantly, a 750 psec pulse increases thepeak power of the pulse by a factor of 6 compared to a 5 nsec (5,000psec) pulse. Thus, to keep the fluence the same and avoid damaging theoptical components of the OPO, the beam area must also be increased by afactor of 6.6 and the beam diameter by a factor of 2.6. This wouldresult in a cavity Fresnel number of N=9080 and a beam quality ofM²>500.

The present applicants have developed an OPO usable in picosecond lasersystems that is adapted to overcome the limitations of conventionaldesigns while maintaining high beam quality.

FIG. 8 is a schematic view of the optical elements of an opticalparametric oscillator 800 according to one embodiment of the presentinvention. The OPO is adapted to be used in dermatological lasertreatment systems having pulse energies of 50 mJ/pulse or higher. A pumplaser providing pulses 810 is used to induce parametric amplificationwithin a nonlinear crystal 830 to produce OPO signal pulses 840 and OPOidler pulses 850. The wavelengths of both the OPO signal pulses 840 andthe OPO idler pulses 850 may be adjusted (or tuned) to achieve a desiredwavelength with a wide range of possible wavelengths. Adjustments may bemade, in different embodiments, by alteration of the crystal orientation(e.g., angle relative to the optical axis) or temperature.

For dermatological applications the ability to selectively damage targettissues or tissue structures is strongly determined by laser wavelength.Accordingly, embodiments according to the present disclosure offer thepotential to select a desired wavelength within a wide range ofavailable wavelengths to obtain the optimum wavelength for a particulartarget tissue or structure, in stark contrast to current dermatologicalapproaches where the available wavelengths are limited to the atomicemission lines of the laser material being used and its harmonicwavelengths.

As already noted in connection with FIG. 6, in various embodiments ofthe invention the OPO 800 may be located in a console or housing, or inan applicator such as a handpiece. In some embodiments, the OPO 800 islocated in the console or housing to enable wavelengths to be rapidlychanged by a user and to enable the use of an articulated arm to deliverany of the available wavelengths to a single handpiece. The dimensionsof typical articulated arms are about 15-20 mm ID and 1.5 meter length,and require a beam to have a beam quality of M²˜100 to avoid clippingthe beam (because of beam divergence) inside the articulated arm.Accordingly, it is necessary to improve beam quality from M²>500 toM²˜100, without relying on multiple crystals or extending the cavitylength beyond 10 mm.

The present invention provides those results in a single-crystal designthat, contrary to prior designs, enables absorption of the OPO idlerpulse wavelength within the OPO crystal to improve beam qualitysufficiently to enable delivery through an articulated arm.

Referring again to FIG. 8, in one embodiment, nonlinear crystal 830comprises a BBO (beta barium borate) crystal positioned between a pairof flat mirrors 820, 840 defining the OPO optical cavity. In oneembodiment, a first mirror 820 serves as an input coupler and has hightransmission (HT) at 532 nm and is highly reflective (HR) at the OPOsignal wavelength, which in various embodiments may range from 575-750nm, 620-720 nm, 660-680 nm, and about 670 nm. A second mirror 840 servesas an output coupler and transmits a portion of the signal wavelength.Second mirror 840 may be constructed to achieve a desired signaltransmission from, e.g., 10-99%, preferably 25-75%, more preferably40-60%, more preferably about 50%. The pump pulse width (or duration)may range from 1 psec to 1 nsec, preferably 100 psec to <1 nsec, morepreferably 500-750 psec. In various embodiments, nonlinear crystal 830may have a length of 5-25 mm, preferably 5-15 mm, and more preferablyabout 10 mm. In one embodiment, the pump beam has a diameter between 4and In one embodiment, the pump beam has a diameter between 4 and 15 mm,more preferably about 10 mm.

The OPO 800 may have an efficiency of about 25% or higher, preferably35% or higher. In one embodiment, OPO 800 is capable of receiving pumplaser input pulses 810 at a wavelength of from 525-535 nm and having apulse energy of 100 mJ/pulse to 5 J/pulse, and outputting OPO signalpulses 850 having a wavelength of from 620 nm to 720 nm and a pulseenergy of about 50 mJ/pulse to about 2.5 J/pulse. In one embodiment, OPO800 is capable of receiving pump laser input pulses 810 at a wavelengthof from 525-535 nm and having a pulse energy of 100 mJ/pulse to 1J/pulse, and outputting OPO signal pulses 850 having a pulse energy ofabout 25 mJ/pulse to about 500 mJ/pulse. In some embodiments, the OPO iscapable of outputting both OPO signal pulses 850 and OPO idler pulses860. In some embodiments, all or a portion of the OPO idler pulses areabsorbed in the nonlinear crystal 830. In one embodiment, the nonlinearcrystal may absorb from 10-75% of the OPO idler pulse energy, morepreferably from 20-60% of the OPO idler pulse energy.

The signal and idler wavelengths λ_(s) and λ_(i) are related to the pumpwavelength λ_(p) by energy conservation through the equation

$\frac{1}{\lambda_{p}} = {\frac{1}{\lambda_{s}} + \frac{1}{\lambda_{i}}}$

For a given pump wavelength, increasing the signal wavelength willdecrease the idler wavelength and vice versa. In cases whereoptimization of the signal is desired, idler absorption may be used toreduce the M² of the signal (i.e., to improve signal quality) and theOPO may be adjusted to a signal wavelength where the idler experiencessufficient absorption to reduce the M² to support practical beamdelivery to the patient surface. When the OPO is located within thehousing of the system, an M² of ˜100 is desirable to allow for areasonably narrow arm diameter that such that the arm is ergonomic andnot too costly. Even when the OPO is located in the applicator, it maybe desirable to use idler absorption to help limit the M² in order tosupport a practical working distance and avoid the need for highnumerical aperture optics within the applicator.

In one embodiment, BBO is used for the OPO crystal material since thetransmission of BBO drops gradually from 100% at 2000 nm to <5% at 3500nm. Using the equation above, we see that signal wavelengths from 630 to730 nm will produce idler wavelengths of between 3420 and 1961 nm for a532 nm pump. Higher idler absorption improves the M² but will alsoreduce the signal output energy. Therefore, a range of red wavelengthsare possible and can be selected depending on the relative importance ofsignal pulse energy and M² for a given application. In on embodiment,transmission through an articulated arm facilitated by selection of 670nm as the OPO signal wavelength, in which case the M² will be ˜100 andsingle-pass idler absorption is ˜30%.

In various embodiments, the present invention relates to the subjectmatter of the following numbered paragraphs.

100. A dermatological treatment system for removal of one or more oftattoos and pigmented lesions using pulsed laser light, comprising:a laser engine capable of outputting first laser pulses having a firstwavelength in the near-infrared region of the electromagnetic spectrum,a pulse width of 100 psec to 1 nsec, and a first pulse energy in therange of 100 mJ/pulse to 10 J/pulse;a second harmonic generator (SHG) capable of receiving the first laseroutput pulses and generating second harmonic laser pulses having asecond wavelength in the green region of the visible electromagneticspectrum;an optical parametric oscillator (OPO) capable of receiving the secondharmonic laser pulses and generating OPO signal pulses having awavelength in the red region of the visible electromagnetic spectrum andOPO idler pulses having a wavelength in one of the near-infrared andinfrared regions of the electromagnetic spectrum; and an applicatorcapable of receiving a selected one of the first laser pulses, thesecond harmonic laser pulses, and the OPO signal pulses and applying theselected pulses to the skin of a patient.101. The dermatological treatment system of claim 100, wherein thesecond harmonic generator is capable of generating second harmonicpulses having a pulse energy in the range of from 50 mJ/pulse to 5J/pulse.102. The dermatological treatment system of claim 101, wherein the OPOis capable of OPO signal pulses having a pulse energy in the range offrom 25 mJ/pulse to 2.5 J/pulse.103. The dermatological treatment system of claim 101, wherein the laserengine, the SHG, and the OPO are capable of generating laser lightpulses having a fluence of up to 5.0 J/cm².104. The dermatological treatment system of claim 101, wherein the laserengine, the SHG, and the OPO are capable of generating laser lightpulses having a fluence within the range of 3.0 J/cm².

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Embodiments of the present invention disclosed andclaimed herein may be made and executed without undue experimentationwith the benefit of the present disclosure. While the invention has beendescribed in terms of particular embodiments, it will be apparent tothose of skill in the art that variations may be applied to systems andapparatus described herein without departing from the concept, spiritand scope of the invention. Examples are all intended to benon-limiting. It is therefore evident that the particular embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the invention, which arelimited only by the scope of the claims.

What is claimed is:
 1. A dermatological treatment system for removal ofone or more of tattoos and pigmented lesions using pulsed laser light,comprising: a laser engine capable of outputting first laser pulseshaving a first wavelength in the near-infrared region of theelectromagnetic spectrum, a pulse width of 100 psec to 1 nsec, and afirst pulse energy in the range of 100 mJ/pulse to 10 J/pulse; a secondharmonic generator (SHG) capable of receiving the first laser pulsesfrom the laser engine and generating second harmonic laser pulses havinga second wavelength in the green region of the visible electromagneticspectrum; an optical parametric oscillator (OPO) capable of receivingthe second harmonic laser pulses and generating OPO signal pulses havinga third wavelength in the red region of the visible electromagneticspectrum and OPO idler pulses having a fourth wavelength in one of thenear-infrared and infrared regions of the electromagnetic spectrum; anapplicator capable of receiving a selected one of the first laserpulses, the second harmonic laser pulses, and the OPO signal pulses andapplying the selected pulses to the skin of a patient; a user-selectablefirst output path located between the laser engine and the SHG, whereinthe user may select the first output path to output first laser pulsesto the applicator; a user-selectable second output path located betweenthe SHG and the OPO, wherein the user may select the second output pathto output second harmonic laser pulses to the applicator; and auser-selectable third output path located proximate the OPO signaloutput, wherein the user may select the third output path to output OPOsignal pulses to the applicator.
 2. The dermatological treatment systemof claim 1, wherein the second harmonic generator is capable ofgenerating second harmonic pulses having a pulse energy in the range offrom 50 mJ/pulse to 5 J/pulse.
 3. The dermatological treatment system ofclaim 2, wherein the OPO is capable of generating OPO signal pulseshaving a pulse energy in the range of from 25 mJ/pulse to 2.5 J/pulse.4. The dermatological treatment system of claim 1, wherein the laserengine, the SHG, and the OPO are capable of generating laser lightpulses having a fluence of up to 5.0 J/cm².
 5. The dermatologicaltreatment system of claim 1, wherein the laser engine is capable ofoutputting first laser pulses having a first wavelength of from 1000 nmto 1200 nm.
 6. The dermatological treatment system of claim 5, whereinthe laser engine is capable of outputting first laser pulses having afirst wavelength of from 1050 nm to 1070 nm.
 7. The dermatologicaltreatment system of claim 1, wherein the SHG is capable of generatingsecond harmonic laser pulses having a second wavelength of from 500 nmto 600 nm.
 8. The dermatological treatment system of claim 7, whereinthe SHG is capable of generating second harmonic laser pulses having asecond wavelength of from 525 nm to 535 nm.
 9. The dermatologicaltreatment system of claim 8, wherein the OPO is capable of generatingOPO signal pulses having a third wavelength in the range of 660 nm to680 nm.
 10. The dermatological treatment system of claim 9, wherein theOPO is capable of generating OPO signal pulses having a third wavelengthin the range of 665 nm to 675 nm.
 11. The dermatological treatmentsystem of claim 1, further comprising: a user-selectable fourth outputpath located after the OPO, wherein the user may select the fourthoutput path to output OPO idler pulses to the applicator.
 12. Thedermatological treatment system of claim 1, wherein the OPO is capableof generating OPO idler pulses having a fourth wavelength in the rangeof about 3420 nm to about 2037 nm.
 13. The dermatological treatmentsystem of claim 1, wherein the OPO is adjustable such that a user mayadjust the OPO to generate OPO signal pulses having a desired thirdwavelength within the range of 630 nm to 720 nm, and corresponding OPOidler pulses having a fourth wavelength within the range of about 3240nm to about 2037 nm.
 14. The dermatological treatment system of claim 1,wherein the OPO comprises: a resonant cavity including a beta bariumborate (BBO) crystal; a first mirror coupled to a first end of theresonant cavity; a second mirror coupled to a second end of the resonantcavity; and an adjustment element operable by the user to adjust the OPOto generate OPO signal pulses having a desired third wavelength and OPOidler pulses having a desired fourth wavelength.
 15. The dermatologicaltreatment system of claim 1, wherein the applicator comprises ahandpiece constructed and arranged to be held in the hand of a user andhaving an output to apply a selected one of the first laser pulses, thesecond harmonic laser pulses, and the OPO signal pulses to the skin of apatient, the system further comprising: a housing, wherein the laserengine, the SHG, and the OPO are located within the housing; and anarticulated arm having a proximal end coupled to the housing and adistal end coupled to the handpiece, wherein one or more of the firstlaser pulses, the second harmonic laser pulses, and the OPO signalpulses is selectable to be delivered from the housing to the handpiecethrough an optical medium located in the articulated arm.
 16. Thedermatological treatment system of claim 1, wherein the laser enginecomprises a seed laser and a seed laser amplifier, wherein the seedlaser is capable of outputting pulsed laser light having the firstwavelength, the first pulse width, and a seed laser pulse energy of from100 μJ/pulse to 5 mJ/pulse, and wherein the seed laser amplifierincludes a Nd:YAG crystal and amplifies the output of the seed laser bya gain of 10-1000.
 17. A dermatological treatment system for treatmentof at least one of a tattoo and a pigmented lesion using pulsed laserlight, comprising: a laser engine capable of outputting first laserpulses having a first wavelength in the near-infrared region of theelectromagnetic spectrum, a pulse width of 100 psec to 1 nsec, and afirst pulse energy in the range of 100 mJ/pulse to 10 J/pulse; a secondharmonic generator (SHG) capable of receiving the first laser pulsesfrom the laser engine and generating second harmonic laser pulses havinga second wavelength in the green region of the visible electromagneticspectrum; an optical parametric oscillator (OPO) capable of receivingthe second harmonic laser pulses and generating OPO signal pulses havinga third wavelength in the red region of the visible electromagneticspectrum and OPO idler pulses having a fourth wavelength in one of thenear-infrared and infrared regions of the electromagnetic spectrum; anapplicator capable of receiving a selected one of the first laserpulses, the second harmonic laser pulses, and the OPO signal pulses andapplying the selected pulses to the skin of a patient, wherein theapplicator comprises a handpiece constructed arranged to be held in thehand of a user and having an output for applying the selected pulses tothe skin of the patient; a housing, wherein the laser engine and the SHGare located within the housing; an articulated arm having a proximal endcoupled to the housing and a distal end coupled to the handpiece; auser-selectable first output path located between the laser engine andthe SHG, wherein the user may select the first output path to outputfirst laser pulses to the applicator; a user-selectable second outputpath located between the SHG and the OPO, wherein the user may selectthe second output path to output second harmonic laser pulses to theapplicator; and a user-selectable third output path located proximatethe OPO signal output, wherein the user may select the third output pathto output OPO signal pulses to the applicator.
 18. The dermatologicaltreatment system of claim 17, wherein the OPO is located within thehandpiece.
 19. The dermatological treatment system of claim 17, furthercomprising: a selector to allow a user to select one of the first outputpath, the second output path, and the third output path; and acontroller to control the operation of one or more of the laser engine,the SHG, the OPO, the applicator, and the selector.
 20. A dermatologicaltreatment system for treatment of at least one of a tattoo and apigmented lesion using pulsed laser light, comprising: a laser enginecapable of outputting first laser pulses having a first wavelength inthe near-infrared region of the electromagnetic spectrum, a pulse widthof 100 psec to 1 nsec, and a first pulse energy in the range of 100mJ/pulse to 10 J/pulse; a second harmonic generator (SHG) capable ofreceiving the first laser pulses from the laser engine and generatingsecond harmonic laser pulses having a second wavelength in the greenregion of the visible electromagnetic spectrum; an optical parametricoscillator (OPO) capable of receiving the second harmonic laser pulsesand generating OPO signal pulses having a third wavelength in the redregion of the visible electromagnetic spectrum and OPO idler pulseshaving a fourth wavelength in one of the near-infrared and infraredregions of the electromagnetic spectrum; an applicator capable ofreceiving a selected one of the first laser pulses, the second harmoniclaser pulses, and the OPO signal pulses and applying the selected pulsesto the skin of a patient, wherein the applicator comprises a handpiececonstructed arranged to be held in the hand of a user and having anoutput for applying the selected pulses to the skin of the patient; ahousing, wherein the laser engine, the SHG, and the OPO are locatedwithin the housing; an articulated arm having a proximal end coupled tothe housing and a distal end coupled to the handpiece; a user-selectablefirst output path located between the laser engine and the SHG, whereinthe user may select the first output path to output first laser pulsesto the applicator; a user-selectable second output path located betweenthe SHG and the OPO, wherein the user may select the second output pathto output second harmonic laser pulses to the applicator; auser-selectable third output path located proximate the OPO signaloutput, wherein the user may select the third output path to output OPOsignal pulses to the applicator; a selector to enable a user to selectone of the first output path, the second output path, and the thirdoutput path; and a controller to control the operation of one or more ofthe laser engine, the SHG, the OPO, the applicator, and the selector.